The present invention relates in general to the sealing of an interface between two components such as a housing and an outer cover where the interior of the housing is at an elevated pressure (above atmospheric). More specifically, the present invention relates to the design of a gasket which includes a molded seal and cooperating carrier. The gasket interfaces with the outer cover so as to prevent blowout of the gasket and loss of the sealed interface which has been established b)y the gasket.
Elastomeric gaskets or seals are commonly used to establish a fluid tight interface between two components which are attached to each other or otherwise assembled such that a leakage path could exist. Typically one component contains a fluid which may or may not be at an elevated pressure. An opening in this one component is closed over by the other component and the two are bolted or in some fashion attached together. Even when the interface between the leakage components and the area surrounding the opening is precisely machined, it is possible for fluid to leak through the interface. The leakage probability increases as the pressure of the fluid within the one component increases. The leakage probability also increases as the distance between attachment points or clumping load points increases.
In certain applications the gasket may include a seal and carrier combination which is sandwiched between the two components. The seal which extends around the opening is compressed by the mechanical attachment of the cover to the housing. The compression of the seal establishes a sealed interface around the opening in the housing and between the two components so as to prevent leakage of the fluid which is contained inside the one component. The attachment of the two components is achieved by the use of threaded fasteners which are typically arranged in a spaced-apart pattern such as at the four corners. The carrier includes a corresponding pattern of clearance holes so that the same fasteners which are used to attach the cover to the housing can be used to secure and position the carrier between the cover and housing.
Depending on the spacing between the threaded fasteners and the pressure of the fluid, it is possible for the gasket to experience what is described as "blowout". If the clamping (pressure) load on the gasket is not sufficient to withstand the internal fluid pressure, the gasket can deflect laterally and blowout from its sealed condition, thereby allowing fluid leakage through the interface between the cover and the housing.
One solution to the blowout concern is to reduce the spacing between the threaded fasteners and/or use a metal plate for the carrier with a relatively high strength and rigidity. By strengthening the carrier and by providing more clamping load points, lateral deflection of the carrier and in turn movement of the seal will likely not occur, even at relatively high interior pressures within the one component (i.e., housing). There are, however, any number of situations where it may not be feasible to add additional threaded fasteners so as to shorten the span between clamping load locations. There are also any number of situations where the use of a plastic material instead of metal for the carrier may be desirable. For example, when there are thermal isolation considerations and/or when lower cost is of interest, the use of plastic for the carrier, as opposed to metal, would be preferred. Typically a plastic material would have less strength than metal and accordingly be more likely to experience lateral deflection and deformation to the point of failure, thereby resulting in leakage at the interface.
In order to prevent blowout of the gasket and still enable the use of a plastic material for the carrier, the present invention has been conceived. The present invention provides a novel and unobvious solution which does not require any change to the mounting hole pattern for the carrier nor for the two components which are joined together, such as a cover and housing. If four corners are used for attachment of the cover to the housing and even if the span between clamping load points between corners is significant, the present invention is unaffected and still provides a sealed interface around the opening in the housing. There are two primary embodiments of the present invention, both of which are suitable to achieve the objectives outlined herein.
Since the use of a gasket to seal around an opening is a relatively old technique, a number of patents have issued over the years which disclose gasket arrangements. The following patents are believed to provide a representative sampling of these earlier gasket designs and concepts:
______________________________________ PATENT NO. PATENTEE ISSUE DATE ______________________________________ 2,981,247 Gaebler Apr. 25, 1961 3,063,439 Kessel Nov. 13, 1962 3,663,740 Dellett May 16, 1972 4,101,138 Gaggiano Jul. 18, 1978 4,784,396 Scott et al. Nov. 15, 1988 4,819,953 Joh Apr. 11, 1989 5,121,933 Silvers Jun. 16, 1992 5,221,097 Ishikawa et al. Jun. 22, 1993 5,377,643 Schibalsky Jan. 3, 1995 ______________________________________
While a variety of gaskets are disclosed by these listed patents, the key features of the present invention are not envisioned.